Scavenger receptor class B type I is required for efficient glucose uptake and metabolic homeostasis in adipocytes

Abstract

Obesity is a worldwide epidemic and places individuals at a higher risk for developing comorbidities that include cardiovascular disease and type 2 diabetes. Adipose tissue contains adipocytes that are responsible for lipid metabolism and reducing misdirected lipid storage. Adipocytes facilitate this process through insulin-mediated uptake of glucose and its subsequent metabolism into triglycerides for storage. During obesity, adipocytes become insulin resistant and have a reduced ability to mediate glucose import, thus resulting in whole-body metabolic dysfunction. Scavenger receptor class B type I (SR-BI) has been implicated in glucose uptake in skeletal muscle and adipocytes via its native ligands, apolipoprotein A-1 and high-density lipoproteins. Further, SR-BI translocation to the cell surface in adipocytes is sensitive to insulin stimulation. Using adipocytes differentiated from ear mesenchymal stem cells isolated from wild-type and SR-BI knockout (SR-BI-/-) mice as our model system, we tested the hypothesis that SR-BI is required for insulin-mediated glucose uptake and regulation of energy balance in adipocytes. We demonstrated that loss of SR-BI in adipocytes resulted in inefficient glucose uptake regardless of cell surface expression levels of glucose transporter 4 compared to WT adipocytes. We also observed reduced glycolytic capacity, increased lipid biosynthesis, and dysregulated expression of lipid metabolism genes in SR-BI-/- adipocytes compared to WT adipocytes. These results partially support our hypothesis and suggest a novel role for SR-BI in glucose uptake and metabolic homeostasis in adipocytes.